The needs for travel and consumer goods have driven the ever increasing consumption of fossil fuels such as coal and oil, typically obtained from deep underground. The extraction of fossil fuels by mining and drilling has often been accompanied by environmental and political costs. Furthermore, as the more accessible sources of fossil fuels are being used up; this has led to the pursuit of more expensive extraction technologies such as fracking and deep sea drilling. Additionally, the consumption of fossil fuels causes higher levels of atmospheric carbon, typically in the form of carbon dioxide.
To reduce these problems, there have been extensive efforts made in converting biomass to fuels and other useful chemicals. Unlike fossil fuels, biomass is renewable and carbon-neutral; that is, biomass-derived fuels and chemicals do not lead to increased atmospheric carbon since the growth of biomass consumes atmospheric carbon.
Much of the work on biomass has involved converting refined biomass including vegetable oils, starches, and sugars; however, since these types of refined biomass may alternatively be consumed as food, there is even a greater utility for converting non-food biomass such as agricultural waste (bagasse, straw, corn stover, corn husks, etc.), energy crops (like switch grass and saw grass), trees and forestry waste, such as wood chips and saw dust, waste from paper mills, plastic waste, recycled plastics or algae, in combination sometimes referred to as cellulosic biomass. Biomass generally includes three main components: lignin, hemicellulose, and cellulose.
Generating fuels and chemicals from biomass requires specialized conversion processes different from conventional petroleum-based conversion processes due to the nature of the feedstock. High temperatures, solid feed, high concentrations of water, unusual separations, and oxygenated by-products are some of the features of biomass conversion that are distinct from those encountered in petroleum upgrading. Thus, despite extensive efforts, there are many challenges that must be overcome to efficiently produce chemicals or fuels from biomass.
A variety of biomass-derived polymeric materials such as lignin, cellulose, and hemicellulose, can be pyrolyzed to produce mixtures of aromatics, olefins, carbon monoxide (CO), carbon dioxide (CO2), water, and other products. A particularly desirable form of pyrolysis is known as catalytic fast pyrolysis (CFP) that involves the conversion of biomass in a catalytic fluid bed reactor to produce a mixture of aromatics, olefins, and a variety of other materials. The aromatics include benzene, toluene, xylenes (collectively BTX), and naphthalene, among other aromatics. The olefins include ethylene, propylene, and lesser amounts of higher molecular weight olefins. CO is another valuable product that can be produced from biomass.
The raw effluent from a CFP process is a complex mixture that comprises aromatics, olefins, oxygenates, paraffins, H2, CH4, CO, CO2, water, char, ash, coke, catalyst fines, and a host of other compounds. Separation and recovery of the various components from this complex mixture present challenges that have not been solved satisfactorily. Recovery of CO from such a complex raw effluent mixture has not been reported.
In U.S. Pat. No. 6,342,091, a process is described for removal of CO2, sulfur compounds, water, and aromatic and higher aliphatic hydrocarbons from industrial gases operated at elevated pressures. At least one morpholine derivative is used as the absorbent, and absorbent vapor is used as a stripping gas to remove CO2 and other materials from the absorbent solvent. The latter process does not address a catalytic pyrolysis product mixture or the use of selective solvents. In U.S. Pat. No. 7,982,077, a process is described for separating CO2 and sulfur containing materials from a paraffin-rich product stream from a high pressure hydrogenation and hydrodeoxygenation process using an amine absorber. The latter process does not recover a CO stream. In U. S. Patent Publication No. 2009/0077868A1, a process is described for separating CO2 and sulfur-containing materials from a paraffin-rich product from a high pressure hydrogenation and hydrodeoxygenation process using an amine absorber and recycle of the sulfur compounds. The latter process does not address recovering CO. U.S. Pat. No. 8,535,613 describes an apparatus for separating acidic gases, CO2 and H2S, from syngas by converting CO in the syngas into CO2 and removing H2S contained in the syngas by using a solvent for physical absorption. No CO recovery is attempted. In U. S. Patent Publication No. 2009/0133437A1, a process is described for separating a CO-rich stream from a stream containing hydrogen, CO, methane, and heavier components through a series of cryogenic separations. The latter process does not use solvent.
In U. S. Patent Publication No. 2014/0107306 A1, a method and apparatus are described for pyrolysis of biomass and conversion of at least one pyrolysis product to another chemical compound. The latter method comprises feeding a hydrocarbonaceous material to a reactor, pyrolyzing within the reactor at least a portion of the hydrocarbonaceous material under reaction conditions sufficient to produce one or more pyrolysis products, catalytically reacting at least a portion of the pyrolysis products, separating at least a portion of the hydrocarbon products, and reacting a portion of the hydrocarbon products to produce a chemical intermediate. A stream rich in CO is not recovered in the latter method.
In U.S. Pat. No. 8,277,643, U. S. Patent Publication No. 2012/0203042 A1, and U. S. Patent Publication No. 2013/0060070 A1, each incorporated herein by reference, apparatus and process conditions suitable for CFP are described. A stream rich in CO is not recovered in the described processes. Similarly, U. S. Patent Publication No. 2013/00324772 A1 discloses a process which may comprise sending the gaseous fraction of a reaction product to a vapor recovery system, but a stream rich in CO is not recovered in the process.
In light of current commercial practices and the disclosures of art, a simple economical process for separating and recovering CO from the product effluent of a catalytic pyrolysis process is needed. The present invention provides such a process.